The present invention relates generally to a capacitor electrode having an uneven surface and used in a semiconductor device. More particularly, the present invention relates to manufacturing a capacitor which has a lower electrode having an uneven surface formed by using Hemispherical Grained Silicon (HSG-Si).
A Dynamic Random Access Memory (DRAM) device is a semiconductor device in which data can be stored and retrieved randomly. As a memory cell of the DRAM device, a memory cell comprising one transfer transistor and one capacitor is widely used. This is because, such memory cell has a simple structure and is suitable for use in a semiconductor device having high integration degree.
According to an everlasting increase in an integration degree of a semiconductor device, a capacitor having three dimensional structure has been developed and utilized as a capacitor for such memory cell. This is because, in a semiconductor device having a high integration degree, it is necessary to enlarge a surface area of each capacitor electrode within a reduced capacitor area in the semiconductor device.
Until now, various structures for the above-mentioned capacitor electrode are proposed, and some of them are practically used. Among them, there is known a technology proposed in a paper entitled as xe2x80x9cHemispherical Grained Silicon (HSG-Si) Formation on In-Situ Phosphorous Doped Amorphous-Si Using the Speeding Methodxe2x80x9d, Solid State Devices and Materials, 1992, pp. 422-424. Hereafter, this technology is called HSG technology, and xe2x80x9cHemispherical Grained Siliconxe2x80x9d is abbreviated to HSG-Si. The HSG technology is used as a technique for increasing a surface area of a lower electrode of a capacitor by forming unevenness on the surface of the lower electrode. It is considered that this technology is effective even in a DRAM device which has a memory capacity of 4 Giga-bits or so and in which fundamental design rule of a semiconductor element becomes approximately 0.13 xcexcm.
There are many kinds of practical methods of forming a capacitor electrode by using the HSG technology. For example, Japanese patent laid-open publication No. 11-163274 proposes a method of efficiently forming uneven surface of an information storing electrode (hereafter, referred to as a lower electrode) of a capacitor by using HSG-Si.
With reference to the drawings, an explanation will be made on a conventional method of forming a lower electrode of a capacitor which is disclosed in the above-mentioned Japanese patent laid-open publication No. 11-163274. FIG. 8 is a cross sectional view showing a schematic structure of a lower electrode of a conventional capacitor, that is, a conventional stacked capacitor. FIG. 9 is a flow chart of manufacturing process showing a conventional method of forming unevenness on the surface of the lower electrode by using HSG-Si which comprises hemispherical grains of silicon.
First, with reference to FIG. 8, an explanation will be made on a lower electrode in which unevenness is formed on the surface thereof by using HSG-Si, that is, which has an uneven surface formed by using HSG-Si. A silicon substrate 101 is prepared. A diffusion layer 102 for capacitor, or a capacitor diffusion layer 102, is formed in the silicon substrate 101 in the proximity of the surface of the silicon substrate 101. An interlayer insulating film 103 which comprises a silicon oxide film is formed on whole area of the silicon substrate 101. The interlayer insulating film 103 is selectively removed to form a contact hole 104 reaching the surface of the diffusion layer for capacitor 102. Then, a lower electrode 105 is formed which electrically connects to the diffusion layer for capacitor 102. Thereafter, a surface unevenness portion 106 is formed on the surface of the lower electrode 105. FIG. 8 shows a structure obtained in this way.
Next, with reference to FIG. 9, an explanation will be made in more detail on a conventional method of forming the lower electrode 105 having the above-mentioned surface unevenness portion 106. After forming the contact hole 104 as mentioned above, an amorphous silicon film (hereafter referred to as a-Si film) is formed on the interlayer insulating film 103 such that the contact hole 104 is filled with material of the a-Si film. The a-Si film is deposited by using a reduced pressure chemical vapor deposition (CVD) method which uses mixed gas of monosilane (SiH4) and phosphine (PH3) or mixed gas of disilane (Si2H6) and phosphine (PH3), as reaction gas. The a-Si film is then microfabricated by using photolithography technology and dry etching technology. That is, the a-Si film is patterned to form the lower electrode 105 (step S101).
Then, the workpiece, that is, the semiconductor substrate, undergoes cleaning by chemical solution such as acid solution and the like (step S102). Thereby, a trace of heavy metal or particles are removed. Then, an oxide film, that is, a native oxide film, formed on the surface of the patterned a-Si film is removed (step S103). After these processing steps, the workpiece, that is, the silicon substrate 101 is inserted into a reaction furnace having high vacuum condition. In this reaction furnace, HSG nuclei are formed on the surface of the a-Si film which is patterned as mentioned above, and are heat treated to form a HSG-Si portion (step S104). The HSG-Si portion thus formed constitutes the surface unevenness portion 106 illustrated in FIG. 8. Also, by this heat treatment, the patterned a-Si film is polycrystalized to become the lower electrode 105 which includes phosphorus impurities.
However, the above-mentioned conventional method of forming the lower electrode of a capacitor has the following disadvantage.
In a mass production process of DRAM""s which uses lower electrodes having surface unevenness formed by using the HSG-Si, that is, hemispherical grains of silicon, as capacitor electrodes, the following disadvantage occurs. That is, there is a possibility that the surface unevenness is not formed uniformly on the surface of the lower electrode. If the unevenness is not formed uniformly, capacitance values of the capacitors vary, and may become out of standard. Therefore, there is a possibility that many defective devices are produced.
The inventor of this invention considered the causes of the above-mentioned disadvantage in detail. As a result thereof, the inventor found the following. In the above-mentioned heat treatment process or processes in which the HSG nuclei are formed on the surface of the a-Si film and further the HSG-Si portion is formed, moisture separates or is released from a semiconductor substrate, especially from an interlayer insulating film. The inventor found that the moisture separated from the semiconductor substrate has a great influence on the formation of the unevenness on the surface of the lower electrode. As will be mentioned in detail later, the moisture separated from the semiconductor substrate causes generation of Si-O bonds or couplings on the surface of the a-Si film. Unwanted objects including the Si-O bonds finally function so as to prevent formation of the HSG-Si. Thereby, densities of HSG nuclei on the surface of the a-Si film or diameters of hemispherical grains which comprise the HSG-Si may vary.
In a mass production line for semiconductor devices, semiconductor wafers on which many semiconductor devices are to be formed are often temporarily stored in a clean room until they undergo next process steps. While the semiconductor wafers are temporarily stored, moisture is absorbed into an interlayer insulating film comprising a silicon oxide film, in each of the semiconductor wafers, although the quantity of the moisture may be very small. It was also found that most of the moisture released from the interlayer insulating film during the above-mentioned process of forming the HSG-Si portion corresponds to the moisture absorbed into the interlayer insulating film while the semiconductor wafer is temporarily stored.
Therefore, it is an object of the present invention to provide a capacitor used in a semiconductor device and a method of manufacturing a lower electrode of such capacitor, in which the above-mentioned disadvantages of the conventional technologies can be obviated.
It is another object of the present invention to provide a capacitor used in a semiconductor device and a method of manufacturing a lower electrode of such capacitor, in which an HSG-Si film can be formed uniformly and stably on the surface of the lower electrode of the capacitor.
It is still another object of the present invention to provide a capacitor used in a semiconductor device and a method of manufacturing a lower electrode of such capacitor, in which an uneven portion can be formed uniformly and stably on the surface of the lower electrode of the capacitor.
It is still another object of the present invention to provide a capacitor used in a semiconductor device and a method of manufacturing a lower electrode of such capacitor, in which a capacitance value of the capacitor can be precisely controlled to a desired value.
It is still another object of the present invention to provide a capacitor used in a semiconductor device and a method of manufacturing a lower electrode of such capacitor, in which a surface area of the lower electrode of the capacitor can be precisely controlled to a desired value.
It is still another object of the present invention to provide a capacitor used in a semiconductor device and a method of manufacturing a lower electrode of such capacitor, in which a capacitance value of the capacitor can be increased and a manufacturing yield of the capacitor can be improved.
According to an aspect of the present invention, there is provided a method of manufacturing a lower electrode of a capacitor comprising: preparing a semiconductor substrate; forming an insulating film on said semiconductor substrate; forming a silicon film on said insulating film; selectively removing said silicon film to pattern it; heating the semiconductor substrate to remove moisture in the insulating film; after heating the semiconductor substrate to remove moisture in the insulating film, removing an oxide film formed on the surface of the silicon film; after removing the oxide film formed on the surface of the silicon film, forming silicon nuclei on the surface of the silicon film by heating the semiconductor substrate in atmosphere containing silicon compound gas; and growing the silicon nuclei and thereby forming a lower electrode which has hemispherical grains formed on the surface of the lower electrode.
In this case, it is preferable that, in the forming the silicon film on the insulating film, an amorphous silicon film in which impurities are doped is formed on the insulating film.
It is also preferable that the insulating film comprises a film which includes silicon oxide as main component.
It is further preferable that, in the heating the semiconductor substrate to remove moisture in the insulating film, the semiconductor substrate is heated at a temperature in a range between 450 and 500 degrees Celsius.
It is advantageous that the method further comprises selectively removing the insulating film to form an opening portion penetrating the insulating film; and wherein, in the forming the silicon film on the insulating film, the silicon film is formed on the insulating film such that material of the silicon film fills the opening portion and contacts the semiconductor substrate via the opening portion.
According to another aspect of the present invention, there is provided a method of manufacturing a lower electrode of a capacitor comprising: preparing a semiconductor substrate; forming an insulating film on the semiconductor substrate; forming a silicon film on whole surface of the insulating film; removing a native oxide film formed on the silicon film; after the removing a native oxide film formed on the silicon film, forming silicon nuclei on the surface of the silicon film by heating the semiconductor substrate in atmosphere containing silicon compound gas; growing the silicon nuclei and thereby forming hemispherical grains on the surface of the silicon film; and selectively removing the silicon film having hemispherical grains formed on the surface thereof and thereby forming a lower electrode.
In this case, it is preferable that, in the forming the silicon film on whole surface of the insulating film, an amorphous silicon film in which impurities are doped is formed on whole surface of the insulating film.
It is also preferable that the insulating film comprises a film which includes silicon oxide as main component.
It is further preferable that the method further comprises selectively removing the insulating film to form an opening portion penetrating the insulating film; and wherein, in the forming the silicon film on whole surface of the insulating film, the silicon film is formed on whole surface of the insulating film such that material of the silicon film fills the opening portion and contacts the semiconductor substrate via the opening portion.
According to still another aspect of the present invention, there is provided a method of manufacturing a lower electrode of a capacitor comprising: preparing a semiconductor substrate; forming an insulating film on the semiconductor substrate; selectively removing the insulating film to form a trench; forming a silicon film on the insulating film such that the silicon film is deposited on the bottom and side walls of the trench; removing a native oxide film formed on the silicon film; after the removing a native oxide film formed on the silicon film, forming silicon nuclei on the surface of the silicon film by heating the semiconductor substrate in atmosphere containing silicon compound gas; growing the silicon nuclei and thereby forming hemispherical grains on the surface of the silicon film; and selectively removing the silicon film having hemispherical grains formed on the surface thereof and thereby forming a lower electrode.
In this case, it is preferable the insulating film has a multi layer structure comprising a first insulating film and a second insulating film on the first insulating film; wherein, in the selectively removing the insulating film to form a trench, the second insulating film is selectively removed to form a first opening portion constituting the trench, and the first insulating film is exposed at the bottom portion of the first opening portion; and wherein, in the forming a silicon film on the insulating film, the silicon film is deposited on the portion of the first insulating film which expose at the bottom portion of the first opening portion and on the side wall of the first opening portion.
It is also preferable that the method further comprises, after selectively removing the insulating film to form a trench, selectively removing a portion of the first insulating film which exposes via the first opening portion to form a second opening portion smaller than the first opening portion; and wherein, in the forming a silicon film on the insulating film, material of the silicon film fills the second opening portion of the first insulating film and contacts the semiconductor substrate.
It is further preferable that, in the forming the silicon film on the insulating film, an amorphous silicon film in which impurities are doped is formed on whole surface of the insulating film.
It is advantageous that the first insulating film comprises a film which includes silicon oxide as main component.
According to still another aspect of the present invention, there is provided a method of manufacturing a lower electrode of a capacitor comprising: preparing a semiconductor substrate; forming a first insulating film on the semiconductor substrate; forming a second insulating film on the first insulating film, the second insulating film is made of water resistant material; forming a silicon film on the second insulating film; selectively removing the silicon film to pattern the silicon film; removing a native oxide film formed on the surface of the silicon film; after the removing a native oxide film formed on the surface of the silicon film, forming silicon nuclei on the surface of the silicon film by heating the semiconductor substrate in atmosphere containing silicon compound gas; and growing the silicon nuclei and thereby forming a lower electrode which has hemispherical grains on the surface of the lower electrode.
In this case, it is preferable that, in the forming the silicon film on the second insulating film, an amorphous silicon film in which impurities are doped is formed on the second insulating film.
It is also preferable that the first insulating film comprises a film which includes silicon oxide as main component, and the second insulating film comprises a film or films selected from a group of films consisting essentially of a silicon nitride film and a silicon oxynitride film.
It is further preferable that the method further comprises selectively removing the first and second insulating film to form an opening portion which penetrates the first and second insulating film; and wherein, in the forming a silicon film on the second insulating film, the silicon film is formed on the second insulating film such that material of the silicon film fills the opening portion and contacts the semiconductor substrate.
According to still another aspect of the present invention, there is provided a capacitor comprising: a semiconductor substrate; a first insulating film formed on the semiconductor substrate; a second insulating film formed on the first insulating film, the second insulating film is made of water resistant material; a lower electrode which is formed on the second insulating film and which has hemispherical grains on the surface of the lower electrode; a capacitor insulating film formed on the lower electrode; and an upper electrode formed on the capacitor insulating film.
In this case, it is preferable that the first insulating film comprises a film which includes silicon oxide as main component, the second insulating film comprises a film or films selected from a group of films consisting essentially of a silicon nitride film and a silicon oxynitride film, and the lower electrode is formed by heat treating an amorphous silicon layer.